Improvement of PD location in GIS [gas-insulated switchgear]

The measuring system we used consisted of two UHF sensors with a frequency band of 400 MHz∼1500 MHz and a digital oscilloscope with maximum 2 GS/s digital rate in its two channels. The difference in arrival times of UHF signals at two sensors can be measured to assist with locating defects in GIS. The test results in the laboratory indicate that the fault location precision depends on the digital rate of the oscilloscope. On the actual site test, if the sample rate is low, there may not be enough sample plots to recover the real pulse wavefronts, which makes it difficult to identify the arrival times at the two sensors of the first peak of the UHF waveform. In this paper, a new algorithm has been described, which applies cubic spline interpolation to increase points between the two real sample points, and improve the location precision of the time-of-flight method. And then the distance difference between the two waves can be determined by using a cross-correlation function. In addition, application software has been developed to help locate the PD source in GIS.